Process for recovery of constituents of ores



United States Patent 2,885,259 PROCESS FOR RECOVERY OF CONSTITUE'NTS OF ()RES Robert F. McCullough, Glenview, Ill., assignor, by mesne assignments, to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application June 21, 1955 Serial No. 517,060

11 Claims. (Cl. 23-145) This invention relates to the recovery of constituents of low grade phosphate-bearing ores. More particularly, it relates to the rendering of the P 0 constituents of -phos-. phate and aluminum clays such as leached zone material from the Florida pebble phosphate fields, available as fertilizer. Still more particularly, it relates to the recovery of phosphorus, aluminum, uranium and minor values from the leached zone material. Examination of the leached zone material indicates the presence of major mineral phases such as quartz, wavellite and pseudo wavellite with some kaolinite and the like. The present invention is directed to the treatment of ores of which this leached zone material is representative or ore fractions in which the claylike portions predominate.

The following analyses of leached zone material were obtained by averaging the analyses obtained from about 200 drill core samples procured over an area of about 36 square miles in Polk County, Florida. Analyses were as follows:

Percent P 0 8.69 A1 0, 8.68 CaO 6.37 U 0 0.014 Acid insolub 68.72

Since the vast percentage of the acid insoluble material is quartz and since it has a coarser particle size than the other materials contained in the leached zone being mined, it has been found advantageous but not necessary to the invention to split the ore, after suitable comminution if desired, into one fraction of small particles and another fraction of coarser particles. It is not meant by this discussion to infer that the entire leached zone material would not be amenable to processing in accordance with the present invention. However, the solids are usually split at from about 150 mesh up to about 220 mesh after having been slurried with water. Other mesh splits may also be used commensurate with efiicient operation of the comminution and classifying equipment. The fraction containing the particles smaller than this range has been found to be the more valuable fraction, while the fraction containing the particles larger than this range is the fraction which is predominantly :quartz and, therefore, a normally discarded material.

The process :of the present invention preferably is concerned with the solubilizing and recovery of .mineral'values contained in the fraction whose particlesare smaller than'about 1159. mesh. 'Ihefgllowing .tableshows a phases of feldspar, fluorapatite,

2,885,259 Patented May 5, 1959 "ice 2 typical split in mineral values between the +200 mesh fraction and the 200 mesh fraction:

Plus 200 Minus 300 Mineral Value Mesh, Mesh,

percent percent J Leached zone material may be processed either on a so-called as mined basis or a wet basis. v If the leached zone material is to be handled in wet form, the material is slurried to about 25% solids with water in a pit at the mining point, pumped to a plant, and subjected to a series of classification and thickening operations. From the classification step there is segregated a -200 mesh fraction which roughly will constitute between about 25% and about 35% of the original-mined material. This -200 mesh fraction is subjected to thickening and filtering operations to reduce the moisture content. The solids are dried at a temperature of about C; and are then ready for treatment in accordance with this process. If the mining method is a so-called dry mining method, the mined material is conveyed to a plant on belts and passed through a drying unit such as a rotary kiln where the solids emerge at about 100 C. The dry material is then subjected to classification operations such as an air classification operation to recover the '1'200 mesh traction corresponding to that recovered in the wet l ss fi ys e In he We las fi a ion system, th screened out +14 mesh size material is comminuted for liberation of constituents and the comm ul ted material subjected to sizing. The +200 mesh fraction is the preferable starting material for the subsequent Processing of the instant invention.

The P s of e in t n in ention omprises admixing leached zone solids with alkali metal reactants, either prior to or during a calcination operation, in the presence of or in the absence of carbon. This calcination prou s a pr uct of h gh r citra e solubility availability than calcination operations in the absence of additives. If recovery of individual constituents is desired, the calcined admixture after slurrying in water, is digested with. dilute sulfuric acid solution. The process then comprises removal of insoluble material from theaqueous solution of water soluble reaction products, precipitating alum from the aqueous solution, removing precipitated alum from the mother liquor, removing uranium and other'minor values from the mother liquor and recovering the phosphorus values from the resulting aqueous solution.

More in detail the leached zone material is mixed with,

for example, sodium carbonate ,in proportion of leached zone material to alkali metal carbonate between about between about 600 F. and about .2000" F., the temperature level being determined primarily by thedegree of recovery sought as regards the minerals aluminum,

phosphorus and uranium, relatively or individually. If high availability as a fertilizer is desired, then heat treatment in the range of about 1500 F. to about 2000 F. is preferable. Also, if high recovery of phosphate after a leaching operation is sought and the recovery of aluminum, for example, is incidental, the heat treatment again is preferably in the range of 1200 F. to about 2000 F. When recovery of phosphate is to be sacrificed in favor of recovery of minerals such as aluminum, uranium and the like, then heat treatment in the range of between about 700 F., and about 1200" F. ispreferred. This calcination or heat treatment may be carried out in kilns, hearth furnaces and the like. Heat treatment has a marked elfect upon filtration rate which has heretofore been one of the prime deterrents to chemical treatment of leached zone material.

Calcination at temperature for a period of from about one-fourth to about four hours is required to obtain good dissolution of various components in aqueous sulfuric acid leached solution with an economic digestion period. Preferably, the leached zone material is calcined for a period of about one hour.

Calcined admixture is cooled to a temperature below about 300 F. before leaching with aqueous sulfuric acid solution. This may be accomplished by blowing cold air through the material to speed its cooling, quenching in suflicient water to lower the temperature to about 300 F., or simply by storing the calcined product until heat has been dissipated and the admixture is needed for processing.

Calcined admixture is digested with an aqueous solution of dilute sulfuric acid. The calcined material is either slurried into a sulfuric acid solution of proper strength or slurried with water after which sulfuric acid is added to the solids slurry. The acid dilution to some extent is dependent upon the physical characteristics of the resulting slurry, i.e., since it is preferred to stir or otherwise agitate the reaction mix, the slurry should be sufiiciently dilute to permit fluidity and the wetting of the solid particles. In general, the amount of sulfuric acid added is correlated to a large extent to the other reaction conditions of temperature, time of digestion, etc. Depending upon the analyses of the particular leached zone processed, between about and about 30% acidulation is desired.

The percent acidulation referred to is that amount of acid required for stoichiometric conversion of cations to metal sulfates. 100% acidulation is that amount of acid required to convert calcium, aluminum, iron, magnesium, sodium and minor cations to the sulfate salts.

The time of digestion required normally will range between about 0.5 hours and about 6 hours, preferably be tween about 1 hour and about 2 hours. Such digestion times are for operating conditions of atmospheric pressure. Pressures above and below the atmospheric range will vary the reaction time. In general, the higher the pressure employed and the higher the temperature employed, the shorter the contact time required for digestion and dissolution of mineral values. The temperature of digestion at atmospheric pressure conditions generally ranges from about 150 F. to about 210 F. For a digestion time of about 60 minutes, a temperature in the range of about 165 F. to about 185 F. is generally preferred.

- The digested material after treatment with sulfuric acid is filtered to remove the insoluble solids. At this stage of the processing, the slurry to be filtered generally; has a specific gravity in the range of about 1.10 to about 1.35 with about 1.2 to about 1.3 preferred. Filter rates generally vary directly with the heat treatment temperatures, i.e., the higher the calcination temperature, the

higher the filtration rate, although it is not implied that this is a linear function. Filtration rates also will vary with the material being processed. Admixture calcined 4 at a temperature of about 1400 F. will have a filtration rate of about 10 to about 60 gallons of slurry per hour per square foot of filter area. This is comparable to a filter rate of about 1 to about 6 gallons of liquor per hour per square foot of filter area, when the leached zone mate rial is not calcined and When using a disc filter. Filtration is carried out at temperatures as high as practical from an operational point of view. Generally, temperature of slurry is maintained at between about 130 F. and about 200 F. Clear liquor or extract recovered by filtration is admixed with a sulfate of ammonia such as ammonium sulfate or ammonium bisulfate or mixtures of both and cooled to about atmospheric temperature of between about 20 C. and about 30 C. This reaction results in the crystallization of a large proportion of the aluminum present in solution as ammonium alum. In general, a more complete alum removal more cheaply is obtained by increasing the concentration of ammonium sulfate rather than by resorting to lower temperatures. Generally, addition of ammonium sulfate is made to attain a NH /Al (SO mole ratio in the range between about 1.0:1 and about 4.5:1. Ammonium alum crystals are removed from the mother liquor by standard solids-liquid separation procedures. Under some conditions recovery of ammonium aluminum sulfate would not be economic. The decision to recover ammonium aluminum sulfate depends upon the composition of the mineral processed, heat treatment given the mineral and reagent conditions used in the dissolution of desired components. Liquor free of suspended solids is subjected to uranium recovery by use of solvent extraction as the preferred modification. In solvent extraction the solution is preferably first subjected to areduction reaction. This may be accomplished by electrolytic means or by chemical reaction with certain free metals such as iron or other agents capable of reducing the solution potential but not substantially introducing metallic ions detrimental to specification of final products. This reduction reaction is believed to partially, if not completely, reduce the uranium from a hexavalent state to a quadrivalent state. If the addition agent is in solid form, the slurry after several minutes is subjected to a liquid-solids separation to remove the unreacted material therefrom. This may be accomplished through the use of a filter, centrifuge, cy-

clone or other suitable separation device. Preferably iron in the form of filings is used as the reducing agent. Aluminum may be used and in this connection, aluminum could he added prior to alum crystallization so that undissolved aluminum could be recovered directly in the alum circuit. Solvent extraction of the uranium may be employed before or after alum removal in an unreduced or only partially reduced state. The major difierence between the reduced and unreduced solution is that the former required fewer extraction stages.

This extraction or solvent phase is made up of two components, the extractant and the vehicle or extender. The extractant may be one or more of the ortho and/or pyro phosphoric acid esters of the alkyl monohydric alcohols. Phosphoric acid esters of octyl or higher molecular weight alcohols are preferred since they are less water soluble. The extender or vehicle may be any one or more of the common organic solvents, such as benzene, kerosene, mineral spirits, toluene, xylene, carbon tetrachloride and the like. Concentration of extractant in the extender may vary widely. For example, between about 1 and about preferably between about 5 and about 10%. The volume ratios of aqueous phase to organic phase may vary within wide limits, for example, between about 1:1 and about 40:1, preferably between about 3:1 and about 10:1. It is preferred that the contact of the organic phase with aqueous phase be in such apparatus as a mixer extraction column and at a temperature of between about room temperature of 20 C.

and about 60 C.

5 aqueous solution and is treated with aqueous hydrofluoric acid or other mixture capable of precipitating and/or removing the uranium from the organic phase as a fluoride in about 5 molar excess over that required Portions A1, 131' and Cl were tested according tothe procedure specified by the American Association of thcial Agricultural Chemists for determining citrate solubility of the calcined product.

to produce uranium tetrafiuoride. This precipitate, tb- 5. Portions A2, B2 and C2 individually were mixed with gether with its accompanying aqueous phase is separated water to produce slurries of approximately 25% solids from the organic phase and the solid uranium tetraby Weight. To each slurry was added 18 parts by weight fluoride precipitate recovered by filtering, centrifuging or of 98% sulfuric acid per 100 parts of P 0 in the heat the like. treated material.- The acidulated slurries were digested The aqueous solution with or without prior alum for about three hours at a temperature of approximately crystallization and after extraction of the uranium with 165 F. After digestion the insoluble material was filorganic solvent is treated to recover phosphorus, nitrotered from the solution of water soluble reaction prodgen, sulfur and other values which are present in soluucts. Results are shown in the attached table. tion. This aqueous solution may be adjusted in pH or Portions D, E and F were treated in a manner correcrystallized with oxygen containing basic alkaline earth sponding to that for'portions A, B and C, respectively, metal compounds or with such reactants as ammonium except that the calcining temperature was approximately hydroxide or ammonia gas or others which form sub- 1400 F. Results are shown in the attached table. stantially water soluble solvents to give a precipitation Portions G, H and I were treated in a manner cor-' of insoluble values such as aluminum and iron phosphate. responding to that for portions A, B and C, respectively, If the pH of the solution is adjusted above neutral, best x p that the calcining temperature w pp x a ly separation conditions are obtained if the original solul922 F. tion is neutralized to a pH above about -8 and preferably from this data it is apparent that leached zone Inatoabout 10. At this stage, the slurry filters or centrifuges tenal calcined at temperatures above 700 C. in the pres with greater ease. Upon removal of the metal phosphate ence of sodium carbonate has a phosphate content of precipitates, the liquor resulting depending upon the PgO 2'5. markedly superior availability over that of material cal: and ammonia concentration, may be process d t ver cmed 1n the absence of alkaline earth metal carbonate ammonium phosphate values. additlve. It is also apparent that the water soluble P Q The. invention will be further illustrated by the followas measured y dissolution p acid digestion is k ing example. edly superior for the leached zone material calcined in EXAMPLE I 30 the presence of sodium carbonate. Addition of sodium le ch d o at ri l tr t d f h i i carbonate and carbon further increases the quantity of in slurry form was subjected to classification in hydro 2 w c can be extracted with the same quantity of separators to recover an overflow product of -200 mesh sulfuric acid although little increase in citrate solubility standard screen size material in the form of about a is apparent.

Table- Percent Mixture Ratio by Weight Recovered Cal- Citrate in Water Portion cining Soluble, Temp., Percent Leeched Sodium Oar- F. H

Zone Oarbonbon P205 U10! ate 12 2 705 57.2 29 25 12 0 705 61.4 $1 27 25 0 0' 705 58.0 9.4 30 25 12 I 2 1,400 77.6 46 25' 12 0 1,400 77.4 25 51 25 0 0 1,400 47.7 32 2s 25; 12 2 1, 922 94. 9 76 21 25 12 0 1, 922 04.8 52 24 25 0 v 0 1,922 17.2 46 27 5% by weight aqueous slurry. This slurry was subjected to a thickening operation to increase the solids concentration to 25%, then filtered and dried to give a feed material having the following assay:

Percent P405 27.7

Ffigoa 3.2 F 1.7 U303 0.05

The dried product was divided into nine portions identifled as A, B, C, D, E, F, G, H, and 1, respectively.

Portion A without any additives was calcined in a muffle furnace at approximately 705 F. Portion B was mixed with sodium carbonate in the weight ratio of '25 parts leached zone to 12 parts and introduced into the same muflle furnace for heat treatment. Portion C was mixed with sodium carbonate and carbon in the weight ratio of 2521212, respectively, and introduced into the same muffle furnace.

The heat treatment time was for approximately one hour. After calcining portions A, B and C were air cooled to room temperature and divided into portions, A1, A2, B1, B2, C1 and C2, respectively.

Having thus described my invention, what I claim is:

1. The process of recovering mineral values from leached zone material which comprises admixing the material With alkali metalcarbonate, calcining the admixture at a temperature in the range between about 600 F. and about 2000 F., digesting the calcined admixture with dilute sulfuric acid, separating insoluble material from the solution of water soluble reaction products and recovering at least one of the values selected from the group consisting of aluminum, phosphorus and uranium values from said solution.

2. The process of recovering mineral values from leached zone material which comprises admixing the leached zone material with alkali metal carbonate, caloinimg the admixture at a temperature in the range between about 600 F. and about 2000 F., digesting the calcined admixture with dilute sulfuric acid, said acid being added in an amount constituting between about 5% and about 30% acidulation, separating insoluble material from the solution of water soluble reaction products and recovering at least one of the values selected from the group consisting of aluminum, phosphorus and uranium values from said solution.

7 I I I I I I I v vleached zonematerial which= comprises admixing I the I t I and about [:1 by, weight. leached 1 zone material to t i I I I leached zone material with alkali metal carbonate, calv reactant, calcining the admixture at ia temperature. m I I I I 1 mf the admixture at a temperature in the m r he r nge between, about 600 F. and about 2000 n;

' a i I I tween about 600 H and about 2000; F; digesting the I digesting the calc in'ed admixture with diluteg'sulfuric acidgi I I I I I i i I I calcined admixture with dilute sulfuric acid :at a rem-j 5 separating insoluble material from the soiution ofwaterfi I I I I p e'rature' in'the: range between about 150. F. and about, I soluble reaction, products and recovering at least one of;

v I @210" R, saidiacid being-added iii-an} amount constituting: I t e, valuesselected'from the'group' consisting of aluminum, I I I hetwcenabout 5% and about 30% acidulation, separatphosphorus and uranium values from said solution. I i r; II I 3 .i'ng' insoluble material fromthes'olution of iwaterisoluble I I I 9 The process of recovering mineral values from 1 I I l I reaction products and recovering at least one of thejvalues. 10 I leached zone material which I comprises admixing the; I I

I I I I I selected from the group consisting of aluminum,v phos material with alkali metal carbonate, calciningthe admixr I I 3 I i i 'pho'rus anduranium values from said solution. I I I I tureat a temperature in the range between about GOO FJ I 4. The process :of recovering. jminerjal. :values from I I and about 2006? F. digesting the calcined admixture I I l I I leached zone material which comprises ad'nilixilng' the I I with dilute sulfuric; acid,; separating, insoluble material leached'zone material with alkali metal carbonate, callfrom' the 'so l u't ion of water soluble reaction products,

i i I I I cining the admixture at a temperat e in the ra ge b i ad 10 t SQIHtiOIi sulfate; of ammonia; wolihg 1 l l I I I tween about 600 F. and about 2000 F.,' digesting the I I I I solution to crystallizeammonium ,aluxn, I separating I I I I calcined admixture. with dilutesulfuric; acid for a period l ammonium crystals, solvent extracting mother-liquor I I I I I i I I i I 1 4 between about one-half; hour, and about six hour said I I 'W th an'alIkyl eS tcro iP P T h 8614150 I OY f n im I I I I I l l l I I acidbeingadded in an amount constituting between'aboutj a ues; p' fijcipitatin'g the uranium values from an organic I I and about. acidulatiom; separating insoluble'l l isolv'cnit and'anunoniating the extracted aqueoussolution; I i I I 2 I Imatetialjfrom the solution of water-soluble reaction prfocb 'aud drying'the resultant slu rr'y, I I I I I I I I I I I I I 'I v I j I i I I I I nets and recovering at, leastv one of the values selected I i i 10- -ht Pr ss 01, Z 'Q IO IQg minerat vait s: from I -.-.fr om the group consistingcf phosphorus and leached; zone material which comprises, admixing the} I I I I I t I I I I ;urani um.va lu es ;frorIn said solution I v I I I I I I .25 ac d O mat r al with Sodium. carbonate, calcining. I 1 j f j processofEx-eco cling minerals/allies from I 1 the admixtureat; a temperature in'the' range bctvveu I I 'ca'ched zone: materialwhich c mprisesadmiXingitEe" ab t 600'F-' d u 2000 Fu' gc fi fig theflcalciucd' I 2 l =I=leached;zonemateriaiwith attainment c rbenatercau I j I adm x e t t u c dnm acid being; added i cining the jadmixturieiat'a temperaturezintheran'g e beum; an amonntzconstituting; betweenabout i5%- and about? I tween: aboutoom F. nd about 2Q0OR, digesting the 3 013 ul ti n; separating insolubleimaterialffrom the I z I I I I I Q I a j calcined admixture with dilutev sulfiuric acid for. a period I I S lution ojf w ater soluble, reaction products and recover+ l i I I I I I I I I between aboutonef hourand aboutnvo 'hours; said acid I l ugi t least Zone; of thevaiues selected froni'the' groupi f 11 'L I 'I being added in anamount constituting between about I I consist g of aluminum, phosphorusanduraniumvalues i j5.% andjabout30% acidulatiomseparatinginsolubleEnia-f I I I I {f m s id l ti'on y I I I t v I vItcrial from the solution-of water soluble reaction products I I I Th P 0; c$s of recovering mineral values: from I andrecovering; at least one of the names selected from I I leached z ne m terial which. conipiis'es admixing 111cm I I I I I j I I I I thegrou'p o sistingof'aiuminnm hesphom andranim t i l w h, a a i mcta nat a in ng -a m n I I I I I .I I jum'v'alues: nem sis solution I I -2 I I g I I 3; I r a e tem e a u in r s we about I v I I I The process o r n m l from I and about 2000? .F.,' digesting {tlic calcine'd admixture I E j I I v jjleached'z n e material which comprises sizing theleac'hcd 4on t dflme u f rc a i pa a s l b r a i i i, j v j j j ,IIZIQIIIBI material to recover a @200 mesh stanrlard-screen} i I f i m t s l i n: i w r soluble reaction Products, I i- I i i I I L I L s z fraction, admncing' thi fractiorz with alkali metal. car I I I adding t0 the? 8021115011 sulfate 7 of ammohl'a, cooling the I i I 'bon'ate,'calc'ining the admixture at a temperature in the solution to crystallize ammonium alum, Separating the range between about 600 F. and about 2000 F., digest ammonium alum crystals, Solvent extracting mother liquor ing the calcined admixture with dilute sulfuric acid, sepwith eie ester of Phosphoric acid remove uranium arating insoluble material from the solution of water vhluesrprecipitafihg the uranium Values fmm an Organic soluble reaction products and recovering at least one of hhil i the P 0f the extracted q s 50111- the values selected from the group consisting of alumni- II-I:tihhhtoIIIprccipitate 011 and aluminum P p p num, phosphorus and uranium values from said solution. athlg h precipitated Phosphates, then further ammoniat- 7 The process f recovering mineral values j;5ding theresultant solution and drying the resultant slurry. leached zone material which comprises admixing the material with alkali metal carbonate, calcining the ad- References Cited in the file of this Patent mixture at a temperature in the range between about 700 UNITED STATES PATENTS II F. and abQut 1200" F., digesting the calcined admixture 45 961 Lieb-G t al with dilute sulfuric acid, separating insoluble material 1880491 a1 71865" from the solution of Water soluble reaction products and 2176609 1932 recovering at least one of the valuesselected from the 222O790 g -1939 gzrloup consisting of aluminum, phosphorus and uranium 33gb? v g f f g fgg *Qfig I 2,767,045 M Cu ough Oct. 16" 1956 I I g mineral values from 2769 686 McCullou h et al N leached zone material which comprises sizing the leached 2 19 Mccull t 1 I 1956' zone material to recover a 20 0 mesh standard screen i Dug e a Jan. 1958 size fraction, admixing the fraction with a quantity of OTHER REFERENCES alkali metal carbonate in the ratio between about 20:1 RMO-2042, AEC publication, Feb. 28, 1955. I 

1. THE PROCESS OF RECOVERING MINERAL VALUES FROM LEACHED ZONE MATERIAL WHICH COMPRISES ADMIXING THE MATERIAL WITH ALKALI METAL CARBONATE, CALCINING THE ADMIXTURE AT A TEMPERATURE IN THE RANGE BETWEEN ABOUT 600* F. AND ABOUT 2000* F., DIGESTING THE CACINED ADMIXTURE WITH DILUTE SULFURIC ACID, SEPARATING ISOLUBLE MATERIAL FROM THE SOLUTION OF WATER SOLUBLE REACTION PRODUCTS ADN RECOVERING AT LEAST ONE OF THE VALUES SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, PHOSPHORUS AND URANIUM VALUES FROM SAID SOLUTION. 